The present invention relates to a system for controlling a force and particularly a very small force. Such a system is used in a gripping apparatus of a robot, a tactile apparatus, and the like.
Recently, the remarkable progress in factory automation (FA) or flexible manufacturing systems (FMS) has caused a large-scale integration of robots into the manufacturing processes. However, since conventional position control type robots operate regardless of their environment, such robots cannot be applied to semiconductor processes requiring fine structure operations, assembling processes for magnetic heads, inspection processes for soft food or soft materials, and the like. Thus, there is a demand for a system for controlling a very small force in robots, free of the above disadvantages.
For example, in the prior art, in the case of controlling a gripping force, a pressure sensor is provided in a gripping portion of a hand, thereby controlling the gripping force with an open angle of the hand. In this case, it is necessary to switch between position control and force control modes at a certain timing; however, it is difficult to control such a timing. Also, it is nearly impossible to accurately control a very small force, since the hand itself has friction. In addition, since a difference in gain between the position control mode and the force control mode is affected by the speed of motion of the hand, vibration and collision occur at a timing when the hand comes in contact with an object. Thus, it is almost impossible to control a gripping force within a small range. Further, one control circuit and one sensor are required for each of the position control mode and the force control mode, thus increasing the manufacturing cost.